Noble metal alloy catalyst preparation has typically consisted of first preparing or more commonly, purchasing, a noble metal precursor. The precursor was formed by precipitating a noble metal from solution onto a support, reducing the precipitated noble metal to the metal form with a reducing agent, such as formaldehyde. The precursor was the dispersed in a solution of alloying metals and the solvent was boiled away to disperse the alloying metals onto the precursor. Finally, the precursor with the alloying metals was heated in a calciner to alloy the metals.
Noble metal alloy catalysts have been produced without the use of a precursor. These catalysts were produced by precipitating a noble metal compound and alloying metals from solution and using a reducing agent to reduce the noble metal. The solution was then dried and calcined to alloy the metals.
Although this process required less steps, no precursor was formed and all the metals were deposited in one process, it also produced an environmentally harmful waste product. The liquid solution which contained a reducing agent such as formaldehyde had to be disposed of.
However, it was believed that the reducing agent was essential in attaining a high activity catalyst. The reducing agent seemed to precondition the support and/or the noble metal allowing high activity catalysts to be produced. Without the use of the reducing agent, the alloy metal loadings were low and inconsistent, and the catalyst had a low activity.
Additionally, there was a fear that if the noble metal was not reduced to its metal form prior to calcination, the noble metal surface area would be significantly reduced due to sintering, again lowering the resulting catalytic activity.
Therefore, what is needed in this art is an improved method of catalyst production which consistently and predictably produces high performance catalysts through simple, environmentally sound processes.